Degenerative diseases are associated with tissue-localized aggregation of proteins in a variety of morphologies, including fibrillar cross--sheet assemblies referred to as amyloid fibrils. The most prominent neurodegenerative diseases among the elderly, Alzheimer's disease, and the Lewy body diseases (including Parkinson's disease) appear to result from a loss in the balance between protein synthesis, folding to a native functional state or maintenance of the natively unfolded state, aggregation, and degradation. In Alzheimer's disease, the natively unfolded A peptide forms fibrillar aggregates that are the principal component of intracellular and extracellular plaques, along with intracellular deposits of hyperphosphorylated tau. Parkinson's disease is characterized by cytoplasmic a-synuclein aggregates associated with degenerating dopaminergic neurons in the substantia nigra and other brain areas. Clinical observations suggest a correlation between oxidative stress/inflammation, aggregation and degenerative diseases. Past studies have demonstrated that hydrophobic aldehydes derived from oxidative stress, in particular 4-hydroxynonenal and the atheronals, exacerbate aggregation through thermodynamic and kinetic perturbations mediated by covalent and non-covalent modifications of A and a-synuclein, which may help to explain the occurrence of sporadic Alzheimer's and Parkinson's disease. The research proposed herein seeks to understand the effect of hydrophobic aldehydes on the maintenance of protein homeostasis in cells and multicellular organisms and the effect that these covalent modifications have on degenerative disease phenotypes in organismal models of degenerative diseases. Besides evaluating the influence of a new set of common lipid-derived aldehydes on aggregation in the absence and presence of biologically relevant membranes, we will discern their ability to inhibit the biological machinery that maintains organismal protein homeostasis, including the disaggregase activity recently discovered in human cells. We propose new methodology to follow protein aggregation in living human cells and in multicellular organisms using FlAsH fluorophores, to complement a previously developed kinetic aggregation assay in which seeding of aggregation by cell homogenates is the readout. Using these methods, we will assess the influence of the hydrophobic aldehydes on protein aggregation in vivo and discern whether quantification of aggregation in organisms explains toxicity as a function of aldehyde concentration in organisms with low or high levels of aggregation-prone protein expression. Transcriptional analysis of the protein homeostasis network upon aldehyde treatment in the presence of controllable levels of aggregation-prone proteins should provide much insight into the etiology of sporadic neurodegenerative diseases associated with aging, aggregation, and oxidative stress.